The present invention relates to a data storage device that comprises a plurality of disks and heads for reading/writing data on the recording surfaces of disks and a method for controlling such a data storage, and more particularly to a storage device that is capable of preventing its heads from deteriorating during a continuous data read/write and a method for controlling such a storage device.
Well-known data storage devices use an optical disk, magnetic tape, and various other types of media. Among others, a hard disk drive (HDD) is widely used as a storage device for use with a computer and has become one of the storage devices essential to the present-day computer system. Due to its excellent characteristics, the hard disk drive has found increasingly wide applications, including a motion picture recorder/player, a car navigation system reader/recorder, and a removable memory for use in a digital camera.
Owing to recent recording density enhancement, the hard disk drive uses an MR head, which is based on a magnetoresistive (MR) effect, a GMR head, which is based on a giant magnetoresistive (GMR) effect, or an MR read/thin-film write composite head (hereinafter referred to as an MR head). The MR head employs a thin-film head for writing purposes and a DSMR (dual stripe magnetoresistive) head, which comprises two MR elements to produce excellent effects of suppressing thermal asperity (TA) arising out of the contact with a medium, for reading purposes.
In the MR head, the sense current for the read head flows to an extremely thin MR element film. Therefore, the element life is adversely affected because, for example, the element fractures due to temperate-rise-induced electromigration acceleration. The magnetic reader/writer disclosed, for instance, by Japanese Patent Laid-Open No. 3216943 (Patent Document 1) is provided with means for sequentially switching from one magnetic head to another at the time of following so that the cumulative total of the read time, seek time, and positioning data read time for following does not vary from one magnetic head to another. In other words, the magnetic reader/writer described in Patent Document 1 memorizes the read time of each head, and switches from one magnetic head to another so that, for example, the magnetic head number sequentially increases from the minimum to the maximum in accordance with the cumulative total read time and in order to prevent an electrical current from being supplied to a single head for an extended period of time. When the maximum magnetic head number is reached, the magnetic reader/writer switches from one magnetic head to another in an opposite direction so that the magnetic head number sequentially decreases from the maximum to the minimum.
In the hard disk drives for IT use, the head seek operation count and head change count are generally decreased to obtain the maximum sustained data rate. Further, LBAs (logical block addresses) are successively assigned to the cylinder circumference so as to reduce the rotational delay time for head seek operations and head changes. A typical idea of assigning LBAs to a plurality of magnetic disk storage areas will now be described. FIGS. 8 and 9 illustrate a conventional LBA assignment method. FIGS. 8(a) and 9(a) are schematic diagrams that illustrate head changes. FIGS. 8(b) and 9(b) indicate the relationship among the cylinder numbers, head numbers, and LBAs assigned to disks.
FIGS. 8(a) and 8(b) show an example in which one track seek is performed so that frequent head changes are made. As indicated in FIGS. 8(a) and 8(b), head 0 writes data into one track (or reads data from one track) on one recording surface of disk 0. Next, head 1 writes data into one track (or reads data from one track) on the other recording surface of disk 0. In this manner, the head number sequentially changes, for instance, from the lowest (Hd: 0) to the highest (Hd: 3) after each change in the track of each cylinder. After the highest head number is reached, the head number sequentially changes from the highest (Hd: 3) to the lowest (Hd: 0). This manner of LBA assignment to disk recording areas (data format) is employed when the time required for a head change is shorter than required for one track seek or when head deterioration is to be prevented.
In marked contrast to FIGS. 8(a) and 8(b), FIGS. 9(a) and 9(b) show an example in which one track seek is frequently performed to reduce the number of head changes. As indicated in FIGS. 9(a) and 9(b), head 0, which corresponds to one recording surface of disk 0, is used to perform a write in relation to cylinders 7 through 0. The head is then changed to head 1. Head 1 is used to perform a write in relation to cylinders 0 through 7 of the other recording surface of disk 0. In this manner, the number of head changes is reduced to increase the sustained data rate. This method is employed when, for instance, the time required for one track seek is shorter than required for a head change. As described earlier, recently used hard disk drives have a narrow track width due to an increase in the recording density so that the time required for one track seek is reduced. Therefore, the method shown in FIGS. 9(a) and 9(b) is used to raise the sustained data rate.
The format described above is a data format for conventional hard disk drives for IT use. At present, however, the data format including the zone format for IT use is used as is for AV (audiovisual) hard disk drives as well.